Optical probes and techniques for O2 measurement in live cells and tissue

In recent years, significant progress has been achieved in the sensing and imaging of molecular oxygen (O-2) in biological samples containing live cells and tissue. We review recent developments in the measurement of O-2 in such samples by optical means, particularly using the phosphorescence quenching technique. The main types of soluble O-2 sensors are assessed, including small molecule, supramolecular and particle-based structures used as extracellular or intracellular probes in conjunction with different detection modalities and measurement formats. For the different O-2 sensing systems, particular attention is paid to their merits and limitations, analytical performance, general convenience and applicability in specific biological applications. The latter include measurement of O-2 consumption rate, sample oxygenation, sensing of intracellular O-2, metabolic assessment of cells, and O-2 imaging of tissue, vasculature and individual cells. Altogether, this gives the potential user a comprehensive guide for the proper selection of the appropriate optical probe(s) and detection platform to suit their particular biological applications and measurement requirements.